Object : This study was designed to asses the protective effects of Kunneo tang on cognitive decline of the patients with early DAT. Method : Before administered with Kunneotang, 16 patients with early DAT were measured by auditory ERP, MMSE-K and K-DRS. During 12 months the patients with early DAT were administered with Kunneotang. After 12months the patients were measured by the same examinations again. Result : 1. The total score of MMSE-K decreased but it was not significant. 2. The total score of K-DRS increased but it was not significant. Among the five criteria(attention, memory, initiation/perseveration, construction, conceptualization), Initiation/perseveration score signifcantly decreased and there were no significant differences in the other scores. But, memory mean score had a tendency to increase. 3. The latency of ERP P300 component increased but it was not significant and the amplitude of ERP P300 component showed the significant difference. Conclusion : The results suggest that Kunneotang may have protective effects on cognitive decline in the patients with early DAT.